The present invention relates generally to air data sensing systems for use on aircraft. More particularly, the present invention relates to methods of detecting unannunciated errors in air data sensing systems including pairs of air data sensing probes (multi-function probes or MFPs).
Air data systems that calculate the aerodynamic aircraft angle of attack (AOA) and angle of sideslip (AOS) of an air vehicle utilizing independent probes that are not pneumatically coupled, but which have processors for interchanging electrical signals between the probes, are known in the art. These probes are sometimes referred to as multi-function probes (MFPs) or air data sensing probes (ADSPs). One type of MFP is the SmartProbe sold by Goodrich Corporation. Multi-function probes include processing circuitry located at the probe itself as part of its instrument package. During sideslip of the air vehicle, compensation of various local (to the probes) parameters or signals, such as angle of attack and static pressure, is necessary for accurate determination of aircraft angle of attack and other aircraft parameters including determination of altitude from static pressure or other means. This requirement for accuracy in altitude indications is particularly important in Reduced Vertical Separation Minimum (RVSM) space areas of the air traffic control system.
In conventional air data systems, probes on opposite sides of an aircraft can be pneumatically connected so that the pressure signals are averaged between the right side of the aircraft and the left side of the aircraft to provide a static pressure that is xe2x80x9cnearly truexe2x80x9d. In most conventional systems therefore, although corrections are made for Mach number and aircraft angle of attack, it is rare that neglecting sideslip effect will introduce enough error to warrant a correction based on sideslip for the cross coupled probes. However, MFPs are connected only electrically in order to eliminate the need for pneumatic tubing passing between the opposite sides of the aircraft or between probes on the same side of the aircraft. This means that each probe is pneumatically independent, even if it is electrically communicating with other probes.
To provide redundancy in estimations of aircraft AOA and AOS, multiple MFPs are used in an air data sensing system. The multiple MFPs can be used in pairs to define multiple probe systems each having two MFPs as members. A single MFP can be a member of several different probe systems.
It is known that estimations of local AOA at two MFPs in a probe system can be used to predict aircraft AOA and aircraft AOS. It is also know that aircraft AOA and AOS can be calculated or estimated by using the local pressure ratios Psl/qcl, where Psl is the local static pressure and qcl is the local impact pressure (the difference between the total pressure and the local static pressure, PTxe2x88x92Psl) from each of two uniquely located probes. In other words, each two-probe system can arrive at estimations of aircraft AOA and aircraft AOS which are a unique function of the local AOA estimations at the two probes or a unique function of the pressure ratio Psl/qcl. Thus, for an air data system having three MFPs, three separate two-probe systems (i.e., systems A, B and C) can be formed, providing three estimations of the aircraft parameters AOS (i.e., xcex2A, xcex2B and xcex2C) and AOA (i.e., xcex1A, xcex1B and xcex1C). If all three values of either of the parameters agree to within some specified tolerance, it could be determined that there is no problem with any of the probes, transducers or electronics. However, if the three values do not agree, it is possible that there exists an error in one or more of the MFPs. Since each probe system has at least two MFPs contributing to its calculations, it can be difficult to isolate the malfunctioning probe. Consequently, a method of detecting these unannunciated errors in MFP air data sensing systems would be a significant improvement in the art.
The invention is extended to cover systems of probes in which it is desired to isolate poorly performing systems or to isolate errors when only two systems are available for xe2x80x98votingxe2x80x99.
A method of detecting errors in air data sensing systems having multi-function probes being used in combinations to define probe systems includes a step (A) of, for each probe system, making a first prediction of an aircraft parameter as a function of local angles of attack at two member probes of the particular system, and making a second prediction of the aircraft parameter as a function of local pressure ratios at the two member probes of the particular system. A step (B) is performed in which, for each of the probe systems, the first and second predictions of the aircraft parameter are compared to determine whether the first and second predictions are within a predetermined threshold of each other. Then, a step (C) is performed in which, for each of the probe systems, if the first and second predictions of the aircraft parameter are not within the predetermined threshold of each other, then the particular probe system is identified as having a malfunctioning member probe.